1. Technical Field
This invention relates to automotive interior trim structures incorporating a cover for an air bag deployment opening and, in particular, relates to an automobile interior trim structure having a decorative outer skin that includes a reinforced air bag door cover. Further, the invention relates to a method for making the reinforced outer skin.
2. Description of the Related Art
Various types of supplemental involuntary restraint systems (SIRs) are currently being provided by automobile manufacturers to help reduce the extent of personal injuries incurred in automobile accidents. Air bags are increasingly becoming one of the most common and popular SIRs utilized. Air bags are designed to inflate during a collision to restrain forward movement of the driver and/or other occupants to help avoid injurious contact with interior portions of the automobile.
Air bags are typically stowed behind one or more interior trim structures, such as the steering wheel cover, door panel, or passenger side portion of the instrument panel. These interior trim structures must, therefore, be specifically manufactured to permit deployment of the air bag upon a collision being detected. Such manufacturing entails consideration of a multitude of design requirements, such as the functional requirements of the air bag deployment system and the aesthetic requirements of the interior trim structures. Moreover, many of these requirements involve counter-vailing considerations. For example, the air bag should be able to be deployed virtually instantaneously upon a collision being detected. However, it should be stowed in such a manner as to 1) inhibit accidental or intentional tampering that would interfere with its performance and 2) contribute to an overall pleasing interior appearance. In regard to the latter consideration, it is, as a matter of human psychology, undesirable to remind the automobile occupants of the dangers of driving and the existence of the air bag is therefore preferably made entirely invisible.
Interior trim structures used in automotive applications typically comprise a composite article having a foam layer formed between a rigid insert and a decorative outer skin. The insert provides structural reinforcement to the interior trim structure and is used to secure the trim structure within the automobile interior. Because the reinforcing insert is rigid, it either has an opening through which the air bag is deployed or is manufactured with one or more hinges which define one or more doors that open upon the air bag being inflated. The portion of the decorative outer skin that overlies the air bag deployment opening is hereinafter referred to as the air bag door cover.
In the typical air bag deployment scheme, the air bag forces its way out of its stowed position upon expansion. Various arrangements of the interior trim structures have been suggested to accommodate deployment of the air bag in this manner. One such arrangement involves forming the air bag door cover as a unitary part of the outer skin of the interior trim structure and pre-weakening the air bag door cover on its inside (i.e., non-decorative) surface to form a tear seam along which the outer skin will separate under the force of expansion of the air bag.
The outer skin, and therefore the air bag door cover, is typically made from a vinyl material such as a polyvinyl chloride (PVC). At cold temperatures, this vinyl material becomes brittle, increasing the likelihood of cracking of the door cover along the tear seam as well as fragmentation of the door cover upon deployment of the air bag. Conversely, at elevated temperatures, the vinyl skin material has a significantly increased tensile elongation and is therefore more difficult to rupture. Moreover, such elongation during expansion of the air bag can cause separation of the outer skin from the intermediate foam layer, possibly resulting in pieces of foam becoming separated from the foam layer.
As mentioned above, the interior trim structure, of which the air bag door is made a part, typically comprises a foam layer formed between a rigid insert and an outer skin. The air bag deployment opening is covered by an air bag door which can have a structure corresponding to the remainder of the interior trim structure, i.e., the air bag door can comprise a foam layer formed between the outer skin and a hinged, rigid backside which provides reinforcement of the air bag door. Although the rigid backside can aid rupturing of the tear seam upon deployment of the air bag, it is not in direct contact with the air bag door cover in which the tear seam is formed. Rather, it must act through the relatively soft foam layer which decreases its ability to cause the air bag door cover to separate along its tear seam.
Reinforcing members have been used for various reasons in other applications. For example, U.S. Pat. No. 4,455,340, issued Jun. 19, 1984 to T. Okina, discloses a flexible molded foam article having an intermediate reinforcing layer located between a semi-rigid polyurethane foam core and surface layer. The intermediate reinforcing layer is formed from three-dimensional cross-linked polyurethane in the form of a thin elastic film. Additionally, woven fabrics or mats made from such materials as fiberglass have been used as reinforcing layers. U.S. Pat. No. 4,130,614, issued Dec. 19, 1978 to G. E. W. Saidla, discloses a structural foam article formed by pouring a polyurethane resin onto a fiber-reinforcing sheet that is placed over a facing sheet in a mold. The polyurethane resin foams through the fiber-reinforcing sheet and bonds to the facing sheet, resulting in a structural foam article having a polyurethane resin core bonded to a facing sheet with an intermediate layer formed from the fiber-reinforcing sheet and polyurethane resin.